OFFSET
1,3
COMMENTS
First column is 1, representing the single-part {{n}}, last column is P(n), since the all-ones plane partitions form the Ferrers-Young plots of the (linear) partitions of n.
A plane partition of n is a two-dimensional table (or matrix) with nonnegative elements summing up to n, and nonincreasing rows and columns. (Zero rows and columns are ignored.) - M. F. Hasler, Sep 22 2018
LINKS
Alois P. Heinz, Rows n = 1..50
A. Rovenchak, Enumeration of plane partitions with a restricted number of parts, arXiv preprint arXiv:1401.4367 [math-ph], 2014.
E. W. Weisstein, Plane partition.
Wikipedia, Plane partition.
EXAMPLE
This plane partition of n=7: {{3,1,1},{2}} contains 4 parts: 3,1,1,2.
Triangle T(n,k) begins:
1;
1, 2;
1, 2, 3;
1, 4, 3, 5;
1, 4, 7, 5, 7;
1, 6, 10, 13, 7, 11;
1, 6, 14, 20, 19, 11, 15;
1, 8, 18, 33, 32, 31, 15, 22;
1, 8, 25, 43, 56, 54, 43, 22, 30;
1, 10, 29, 66, 81, 99, 78, 64, 30, 42;
...
MATHEMATICA
(* see A089924 for "planepartition" *) Table[Length /@ Split[Sort[Length /@ Flatten /@ planepartitions[n]]], {n, 16}]
PROG
(PARI) A091298(n, k)=sum(i=1, #n=PlanePartitions(n), sum(j=1, #n[i], #n[i][j])==k)
PlanePartitions(n, L=0, PP=List())={ n<2&&return([if(n, [[1]], [])]); for(N=1, n, my(P=apply(Vecrev, if(L, select(p->vecmin(L-Vecrev(p, #L))>=0, partitions(N, L[1], #L)), partitions(N)))); if(N<n, for(i=1, #P, my(pp = PlanePartitions(n-N, P[i])); for(j=1, #pp, listput(PP, concat([P[i]], pp[j])))), for(i=1, #P, listput(PP, [P[i]])))); Set(PP)} \\ M. F. Hasler, Sep 24 2018
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Wouter Meeussen, Feb 24 2004
STATUS
approved